Telephone system



TELEPHONE SYSTEM 1s sheets-sheet 1 Filed July 20, 1940 Feb. 17, 1942,

S. E. PETERSON El AL TELEPHONE ASYSTEM A 13 Sheets-Sheet 2 Filed July 20, 1940 s R can I m www .NmuI l m QQN ooo \ww` NWN WMN QMNI W i Swm; w wi, mhki.. |17 NNN @9N QS 25 mmm Qwm 1 4 EN# /QN a, mmtmmwx @NME @G .wk @t G mt @N2 w Gm mw ww gm Gt .mwh SN. @www mm sETH E. PETERSON IRVIN GEITGEY /WM'M ATTORNEYS Feb. 17, 1942. s. E. PETERSON ETAL TELEHONE' SYSTEM Filed July 20, 1940 15 Sheets-Sheet 5 INVENTORS SETH E. PETERSON IRVIN GEITGEY QMW wf ATTORNEYS Feb. 17, 1942. I s E PETERSQN ETAL 2,273,139 I TELEPHONE SYSTEM Y l5 Sheets-Sheet 4 Fl'ed July 20, 1940 ,SS Y @w (MQW INVENTORS SETH E. PETERSON IRVIN GEITGEY my l f ATTORNEYS Feb. 17, 1942. s. E. PETERSON ETAL TELEPHONE SYSTEM 15 sheds-sheet 5 Filed July 20, 194D wm@ www! m ma s lv@ m mm m T@ m mm n A Smlw www/.Fill m .gmx Q I www@ .www f @Mg @mm/ Il @mi hmmm Qwmmm@ m@ www mu l 902mm, @mmm b F Fwwm www/J. @www @E Qn A m No Rm I|. I @E A m Gm, MSW

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TELEPHONE SYSTEM Filed July 20, 1940 15 Sheets-fSheet 6 Rmb INVENTORS sETH E. PETERSON lRvlN GEITGEY ATTORNEYS Fel 17, 1942 s. E. PETERSON ETAL 2,273,139

TELEPHONE SYSTEM Filed July 20, 1940 13 Sheets-Sheet '7` INVENTORS SETH E. PETERSON IRVIN GEITGEY ,MMI ATTORNEYS ENA RMP PQMN mmm INVENTORS .SETH E PETERSON mvm GEITGEY `ATTORNEYS 13 Sheets-Sheet 8 TELEPHONE SYSTEM S. E. PETERSON ET AL Fil'ed July 20, 1940 Feb. 17, 1942.

Feb- 17, 1942- s. E. PETERSON ET AL 2,273,139

TELEPHONE SYSTEM 15 sheds-sheet 9 QRS@ Filed July 20, 1940 INVENTORS sETH E, PETERSON mvm GEITGEY BY M MM5 ATTORNEYS 13 Sheets-Sheet lO INVENTORS sETH E.PETERsoN lRvm GHTGEY ATTORNEYS S.E.PETERSON ETAL TELEPHoNE'sYsTEM Filed July 20, 1940 @Ski wg l w3 Feb. 17, 1942.

Feb. 17, 1942.

S. E. PETERSON ETAL TELEPHONE SYSTEM 13 Sheets-Sheet y ll Filed July 20, 1940 PETERSON IRVIN GEITGEY INVENTORS ATTORNEYS E wg Q @Rb m @QG md S www s l Feb. 17, 1942. s. E. PETERSON ET AL TELEPHONE SYSTEM Filed July 20, 1940 13 Sheets-Sheet 12 SETH E. PETERSON Feb. 17, 1942. s. E. PETERSON ET AL 2,273,139

TELEPHONE SYSTEM Fileq'July 2o, 1940 15 sheets-sheet 13 INVENTORS SETH E. PETERSON IRVIN GEITGEY #im m ATTORNEYS Jmm l 'Patented Fel .17,`1942` UNITED STATE s1 Y PATE-NT diarios` u TELEPHONE SYSTEM seth E. Peterson, chicago, n1., and Irvin Geitgey,

Elyria, Ohio, assignors nto' Associated Electric Laboratories, Inc., Qhicago, Ill., a corporation of Delaware Y .sppueauon July zo, iaiasexial No. 34am I s4 claims. (c1. 179-21) The present invention relates to telephone systems and has for one oi its objects the provision Y of improved switching apparatus of the charac-l .Y

ter utilized in setting up and supervising connections extending between the substations served by diierent exchanges of a multi-exchange network.

In a system of this character. inter-exchange calls are routed over toll lines and trunks interconne'cting the exchanges. .and the line switching operations which are required in routing the vcalls to the'desired substations-- are f either performed manually at switchboard'sof the manuaLty'pe or are effected on a' semiauto. matickbasis through the provision of tolland local switching equipment of the automatic type which is controllable from the various operators positions. In handling calls of this character.

.the connections are usually routed -through at.

least one and frequently three or more operators positions in' tandem, the diilerent operators positions being located in different exchanges, and.

it is necessary to provide facilities whereby supervisory' signals may be dispatched to the proper operators position or operators positions in response to call answering, connection release and operator recall operations performed at the calling and called substation. In setting up .toll

connections, the use of voice .current ampliers for increasing the voice current transmission level at appropriate points along the toll lines is frequently necessary. In the usual arrangement, wherein a call routed: over one 'of the toll lines to a central exchange may be terminated locally at a substation' served by the central .exchange or extendedover-an iiiter-oilice-truni:

to a substation served by an exchange distant from the central exchange; the .transmission level isincreased by the ampliners associated with the toll line in use by an amount suillcient through which.' the toll line connections are routed. f

It is an object of the present invention toprovide in asystem of the character described. im-

proved facilitieswhereby' the supervision oi calls routed by way o f one` or more tandem connected ,n .operators' positions-may be accomplished inasimple and reliable manner with a minimum o f equipment in the switching apparatus through which the calls are extended. n

It is another object of Ithe invention toprovide in a'. systeml of the character described, which utilizes automatic toll switching apparatus for extending connections Afrom the toll lines, an improved arrangement wlierebyi the voice current transmission .level of the toll lines is selectively and automatically controlled in accordance -with the character of vthe lines to lines. y,

It is another object of the invention toprovide in a system of the character described, improved toll switching apparatus which isso v'connected and arranged Athat the same relay equipment may be utilized for both supervisory and pad control purposes in setting up and supervising. toll calls,lthus minimizing the amount of equip` ment required to eilect these separate and disl tinctends.

Itis another object of the invention to provide in a system of thecharacter described, improved toll switching apparatus which is so connected'.

and arranged that the selective control of the transmission level control pads 'is automatically acccomplished in a simple and reliable manner without any supervision or thought on the partA to compensate for the loss introduced by the presence of -an inter-cnice trunk in thehestabo -lisheszi connection. This, of course, means that v selectively be switched in and out oi' the v oice l currentfchannels to controlthe voice current .:transmission level.' Inv the`usual arrangement `is accomplished manually by keyoperations performed at lone of .the operators? positions positions 'and at YSignal. of diilerent' provide for uscjinasystemof the character de-v scribed, an improvedoperatorsmmk oraccess i circuit which is soxconnected andarranged that" of the' toll operators.

' It is another object of the invention to provide inl a system of the character described, an ar.J rangement whereby a supervisory operation per-- formed bythe 'operator attending one of a plurality 'of vtandem connected operators positions causes a supervisory signal .oi one character to bevtransmitted ove'i the connection to the operator attending a second oi the tandem connectedl character to over the connection to a thirdl Vof"ti'iietandem' connected operators' positiomgjA l It is still another object ot invention. tov

after a connection has. beenfrouted' thereto which connections are extended from the toll.

through associated impulse controlled automatic switching equipment, any further impulse digits transmitted over the connection are utilized smaller exchanges. The switching equipment of the central exchange includes a switchboard at solely for the purpose of controlling the line sig'- nal lamp embodied therein.

It is a further object of the invention to prowhich are provided the usual inward toll, C. L. R.; delayed call, infomation and intercepting operators positions. 'I 'oll calls handled at this 4switchboard are routed to theoperatorsl posivide in a system of the character described, im-l l I proved automatic switching apparatus which comprises toll switching selectors andacces's' or trunk circuits and which is so connected and arranged that the sam control path extending between a selector and an access circuit occupied with a call may be utilized for the. purpose 1 i over the trunksassociated with the access circuits are controlled by timing equipment provided in the preceding selectors.

It is a further object of the` invention to provide in a system of the character described, im-

proved automatic switching apparatus including,

selector switches of the voice current repeating type which have access to succeeding switching units arranged for bothloopcircuit and simplex circuit control over their. incoming trunks, and

I which is so arranged that the voice current repeating elements of the selector switches are only excluded from talking channels established through these switches when the channels are extended through succeeding switching'units arranged for simplex circuit control.-

It (is a still further object of the invention to provide for use in a'system of the character detions and-'extendedftherefi-guirough-automatic tollswitching apparatus' yof fthe Iv'well-*known Strowger type. This apparatus includes toll transmission selectors, toll switching selectors 3K and appropriate operators access circuits and trunkcircuits, and is so arranged that in setting up connections routed'from the toll switching point to the central "exchange, the central exchange isutilized incertain instances as a tandem exchange, the 'assistance of the operators attending the` switchboard in the central exchange not being required. In one case whereinthe central exchange is utilized as a tandem exchange, a connection may be extended,fromme calling toll line througha toll transmissioneselector of the impulse repeatingtype, a toll secv ond selector, a repeater and .additional-auto matic switching equipment f to j the Idesired Aline wn. terminating at the distant exchange. In settin u; up a toll connection of this type,,.the control, equipment of the toll vtransmission*selector is!` held in its impulse repeating rsettinglun'tilall of the digits designating thefdesired ,line have beenv dialed at the calling operatorsposition located',`

at the toll switchingp'oint. .For,thefpurpose of switching thisA controlffequipm'ent Vto fits lringing setting after the dialing operation is completed,v there is provided in 'the'succeeding repeater aiK digit counting device which functions,fafter af predetermined number of digits have been transf..v

mitted to the repeatentojtransmit a signal back i to the toll transmission selector indicating that the dialing operation is ended, whereupon 'the-Q` control equipment of this selector isautomatil cally switched to its ringing or called'line'- signalf ing setting. After this settingis fatmindgthe n scribed, improved automatic switching apparatus which is so arranged that the setting of the control equipment embodied in at least one of the selectors is arranged to be controlled by a digit counting device which is, provided in a succeeding switching unit, such, forexanple, as a succeeding impulse repeater.

It is still another object of the invention to provide in a system of the character described, an arrangement wherein callsrouted to certain lines or substations ofthe system are intercepted and routed to an intercepting operators; position, and wherein 'facilities are provided for transmitting to the interceptin'g'operators position signals which identify callsrrouted thereto from calling toll or trunk lines, and signals are also transmitted over the calling toll or trunk lines for the purpose of informing the calling operators that the calls have been intercepted.

It is astill further-object of the invention to `'provide for use in conjunction with automatic toll switching equipment of the character described, improved alarm signaling equipment which is so arranged that the condition of a connecte'd by means of one-way, ,voice current repeatered Atoll lines with a 4`distant toll point and by means of different groupsy of i inter-cnice trunks with a "plurality of remotely locatedv control equipment of the toll ltransmission se-A lector is selectivelycontrolled by the Aback-bridge` relay of the succeeding repeatenlsothatjit is changed from its ringing setting "to its call an,- swered setting,' or vice versa, each time 'the' 1 switchhook provided at the called" substation is 'l operated between its two operating positions`." Provisions are also made in the yselector lforV i transmitting an appropriate 'v supervisory signal f over the calling toll lineeachtimethe setting of the control equipment is-'changed vfrom one fr of the two last-mentioned settings to theother.

In another instance where'thecentral exp- 1l change is -used as a tandem exchange between,'-'

the toll switching point and "aiother distant exlselector of the train, and provisions are made whereby rering signals may be transmitted over the ring-down trunk and flashing recall signals may be transmitted to the calling operator at the toll switching point. All of these supervisory operations are achieved through the operation of relay equipment which is controlled over the single control path extending between the toll switching selector and the access circuit of the switch train.

Calls originating at the toll switching point may also be routed over the toll lines to the various operators positions in the central exchange, these operators positions having associated therewith appropriate trunk 'or access circuits which are accessible to the toll switchingselectors. `In accordance with another feature of the invention, provisions are made in these access circuits whereby impulse digits transmitted thereto after the seizure .thereof are absorbed, thus permitting a more universal directory numbering scheme to be used. The arrangement of the 'digit absorbing relay equipment is such that this equipment also functions toA control the incoming call signal lamps of the associated operators position circuits.

In accordance with another feature of the invention, the access circuits which are provided in association with the delay operators positions of the central exchange switchboard are arranged to pass supervisory signals to the distant toll switching point. These access circuits are also arranged for the selective control of the toll pad lswitching relays in accordance with the character of the lines to which calls are extended from the delay operators position. The arrangement of the relay equipment embodied in these circuits is such that a single control path,.`yvhich is independent of the talking or communication channel of a connection, may be utilized for both pad switching control and supervisory control purposes. These circuits are also so arranged that when connections are extended therefrom to inter-oice trunks of the ring-down variety requiring the use of alternating current supervisory signals, splashes of ringing eurent transmitted thereto over the extended portions of the ringdown trunk connections cause the production of supervisory signals of one character, namely, steady signals, at .the delay operators position, and supervisoryvsignals of a-different character, namely, intermittent signals of the ashing recall type, at the distant toll switching point.

Further features of the invention pertain to the particular arrangement of the toll switching apparatus and its associated alarm equipment, whereby the above-outlined and additional objects are achieved.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention, both as to its organization and method of operation, together with further ,objects and advantages thereof, will best be understood by reference to the following specification taken in. connection with the accompanying drawings in which Figure 1 illustrates the general arrangement of a telephone system embodying the present invention; Figs. 2 to i3, inclusive, taken together, illustrate th'e details of a system having incorporated therein theA features of the invention as briey .outlined above; and Fig. 14- illustrates the mode of combining Figs. 2 to 13, linclusive, to form a unifled system.

GENERAL DESCRIPTION OF THE SYSTEM Refering now more particularlyto Fig. 1 of the drawings, the telephone system there illustrated comprises a central exchange 20, a remote exchange or toll switching point 30, a distant exchange 40, a distant exchange l0, a C. A. X 50 and a C. A. X 60.' The remote exchange 30, the distant exchange 40 and the distant exchange 'I0 may be of any Well-known type; each serving a number of subscriber. substations, not shown; while the central exchange 20, the-C. A. X 50 and the C. A. X 6D are of the automatic type, each serving a numberA of subscriber substations. More particularly, the central exchange 20 serves a number of subscriber substations including the subscriber substations TI and T4.; the C. A. X 50 serves a number of subscriber substations including the subscriber substation T2; and the C. A. X 60 serves a number of subscriber substations including the subscriber substation T3. The re- Ymote exchange 30 and the central exchange 20 are lnterconencted by a group of one-way toll lines, each of which is equiped with voice current repeaters or amplifiers. Thus the toll line 440, which terminates in the central exchange 20 in a toll line circuit442, is equipped with a number of voice current repeaters 440:1 which function in a well-known manner to raise the voice current level at appropriately spaced points along Ithe length of the line 440. The central exchange 20 is also connected with the distant exchanges l0r of two-way trunk lines, including the trunk line 4I5.

The remote and distant exchanges 30, 40 and I respectively comprise toll operator positions 4M, H60 and H42; while the central exchange 20 comprises an automatic dial switchboard I |50 which includes a plurality of operators positions including an intercepting operators position III, a toll operators position H52, an information operators position H53 and a delay operators 'position H54. As indicated above, each toll line in the group of toll lines extending from the remote exchange 30 to the central exchange terminates at the operators position 44| in the remote exchange and in a toll line circuit in. the central exchange 20. Similarly, each trunk-in the group of trunks extending from the central exchange 20 to the distant exchange 40 terminates in a trunk circuit in the central exchange 20 and at the operators position H60 in the distant exchange 40, the trunk H05 terminating in the trunk circuit I IOI and at the operators position H60. Also each trunk in the group of trunks extending between the C. A. X and the central exchange 20 terminates in automatic switching equipment 403 provided in the C. A. X 50 and in a trunk circuit in the central exchange 20, the trunk 405 terminating in the trunk circuit 404. Each trunk in the group of trunks extending between the C. A. X and the central exchange 20 similarly terminates in automatic switching equipment 4I3 provided in the C. A. X 60 and in a trunk circuit in the central exchange 20, the trunk 4I5 terminating in the miviauauy thereto, the :me su terminating in /the line circuit 692 and the line serving the substation T4 terminating in a similar circuit. It is noted that the subscriber lines terminating vin the C. A. X 50 have access to and are accessible to the automatic switching equipment 403, and the subscriber-lines terminating in the C. A. X 60 have access to and are accessible to the automatic switching equipment 4|3. Also the subscriber lines in the central exchange have access to and are accessible to local switching equipment, not shown, but forming a part pf the automatic switching apparatus, provided in the central exchange 20, i

The central exchange 20 is provided with a toll switching equipment which comprises the sets of toll switching apparatus 420, 430 and H40; a group of toll transmission selectors, including the toll eransmission selector 300; a group of toll second selectors, including the toll second selector 616; a group of toll switchingV selectors, including the toll switching selector 100; a group of toll incoming selectors, including the toll incoming selector 460; and a group of toll connectors, including the toll -connector 68|. Further the toll switch train comprisesa ilrst group of repeaters, including the repeater 600, individually associated with the toll incoming selectors; a second group of repeaters,l including the repeater 686, associated with the automatic switches having access to the trunks extending to the C. A.

' -X SJ; a first group of access circuits, including erators position H53; a delay operators position circuit H30 associated with the delay operators position H54; and a vthird group of access-circuits, including the access, circuit |000, associated with the delay operators position H54. The switching .equipment provided in the central exchange 20 further comprises a call intercepting circuit 693 which is associated with certain of the subscriber lines terminating at the central exchange. 20 and functions :to forward calls routed to these lines to the intercepting operators position I |5|. Alarm equipment 200 is also provided in the central exchange 20 for the purpose of testing and indicating the condition of the associated line switching and auxiliary equip-f ment.

Preferably, the automatic switching equipment 403 provided in theC. A. X 50, the automatic switching equipment 4|3 provided in the C. A. X 60, and the local automatic switching equipment of the central exchange 20, are of the well-known Strowger type although this equipment may bel connected and arranged in any convenient manner. 'I'he toll switching equipment provided in the central exchange in association with the operators positions at the switchboard H50 and including the sets of switching apparatus 420, 430

and |40, may also be of any desired arrange- Patent No. 1,736,041, 'I'harp et al., granted Decem-i ber 23, 1930. Also; the operators position equip'- ment providedat the toll operators position H00 and at the intercepting operators position ||5|,

and the call interceptlng circuit 893, may be of substantially conventional design and arran`ge semmaiv ment.. The repeater 086, the trlmk circuit 404, the trunk circuit 4|'4, the trunk circuit ||0| and the other corresponding repeaters and trunk circuits forming a part of the centralexchange switching apparatus may also be of conventional design and arrangement.

The manner in which calls completed locally through the automatic switching apparatus provided in the C. A. X 50, the C. A. X 60 and the central exchange 20, forms no part of the present invention and, accordingly, an explanation of the details of this apparatus is deemed to be unnecessary. For the same reason, the manner in which toll calls initiated on the lines terminating at the central exchange 20 and routed through the local and toll switching apparatus of the exchange to one of the toll operators positions are handled, and the manner in which calls are transferred through the toll switching apparatus between the various operators positions provided in the switchboard H50, are not disclosed herein since it is believed that the novel features of the system may readily be understood without a detailed explanation of the entire system arrangement. It is noted, however, that the in and out trunks indicated as extending to the toll switching units 420, 430 and ||40 are utilized in setting up connections between the toll operators positions and thc lines terminated locally in the central exchange 20,

The toll line circuits provided in the central exchange 20 to terminate the toll lines extending to the remote exchange 30 are of identical arrangement. The toll line circuit 442 is illustrated in Fig. 13 of the drawings as comprising a 'vom current repeating coil |360, a line or pulsing relay R|300, a retard coil |304, a supervisory relay R|3|0 and associated signal lamp |3|4, a slowto-release hold relay Rl320, a series control relay R|340, a second control relay R|350 which is a `slave to the hold vrelay Rl32'0, a line balancing coil |358 and a transmission pad network |310. This network includes loss resistors which are preferably connected and arranged in the manner disclosed in Fig. 2 of Patent No. 2,167,710, Crocker, granted August 1, 1939, and a .pad switching relay which is arranged to be controlled over the control lead C|309 by a pad control relay R|330. As indicated above, the purpose of this network is to determine the voice current transmission level of a communication channel established through the toll line circuit 442. More specifically, the pad network is provided for a two-fold purpose. One function of this network is to introduce a definite loss in the mmunication channel when the toll lino 440 is connected through the switching equipment of the central exchange 20 to a subscriber line terminating at this exchange. On the other hand, when the toll line 440 is connected through the switching equipment of the central exchange toan inter-ofllce trunk, the loss resistors of the network are. excluded from the communication channel, whereby the transmission level is enhanced to compensate for the loss occasioned by the presence o f the inter-oilice trunk in the connection. The second function of this network is to introduce a circuit loss which tends to balance the artificial line network at the repeater 440a nearest the central exchange regardless of the transmission characteristics of the line to which a connection is extended from the toll line 440. The manner in which the pad switching relay embodiedin the network |310 is automatically controlled in accordance withv the terminating point of a. connection extended to the toll line 400, is pointed out with particularity hereinafter.

The toll transmission selectors provided in the central exchange 20 are of the impulse and voice current repeating type and are identical in arrangement. Thus, the toll transmission selector 300 is illustrated in Figs. 3 and 5 ofthe drawings as comprising a voice current repeating element 3|0 and a switching mechanism 5|0 of the wellknown Strowger type. Brieily described, this mechanism includes a wiper set which isprovided with four wipers,5||, 5|2, 5|3 and 5|6, capable pulsing relay R650, a slow-to-operate hold relay of both vertical and rotary movements, and an f' associated contact bank including ten horizontal levels of contact-sets. The switching mechanism 5|0 further comprises a vertical magnet 520 for moving the wiper setfin a vertical direction, a rotary magnet 52| forv moving the wiper set in a rotary direction, and a release magnet 523 for releasing the wiper set so that it may be returned to rotary and vertical normal. The switching mechanism 5I0 is also provided with a number of auxiliary switch springs which include the vertical off-normal springs 390, the normal post springs 395 and 396, and the 11th step cam or oi-normal springs 391 and 525. These various sets of contact springs are controlled in laccordance with the vertical and rotary movements of R640,` a slow-'acting digit counting relay R630, a

line switching relay R660 and a back-bridge relay R655' of the electro-polarized type.

'I'he access circuits associated with the interoiiice trunks connecting the central exchange 20 with the distant exchange 40 are of the character illustrated in Fig. 8 of the drawings. Briefly described,'.this access circuit includes a voice current'A repeating coil 8|0, a simplex controlled line relay R800, a slow-acting cut-off relay R850, an alternating current recall relay R860, a ringing control relay R010 and a line switching relay R880.

The accesscircuit 900 and associated operators position equipment provided in association -4 with the information operators position |53 are the wipers 5| to MIL-inclusive, in a manner more l fully described hereinafter. The control`V equipment of the toll transmission selector 300 comprises a ballast lamp 3|1 of the double filament type and a group of control relays. More specilically, the relay equipment of the selector includes a switch-through or simplex relay R320, an answer or back-bridge relay R330, a switch-'through or ring position relay R300, a combined battery supply and back-bridge relay R350, a tone relay R355, a loop circuit control relay R350, a slow-tooperate control relay R310, a slow-to-release ring start relay R530, a line or impulsing relay R535, a supervisory relay R550, a sloW-to-release hold relay-R505, a line switching relay R550, a transferrelay R560 of the slow-to-release type, and an automatic cut-in or stepping relay R510. The

manner in which the enumerated relays are connected and arranged is more fully described in the following portion of the specification wherein the details of operation of the selector 300 are explained.

Preferably each of the toll switching selectors provided in the central exchange 20 is identical in arrangement with the toll switching selector 100, illustrated in Fig. '1 of the drawings. Briefly described, this selector comprises a switching mechanism 1|0 which is identical in construction and arrangement with the switching mechanism 5|0 of the toll transmission selector 300, and

- comprises a set of wipers 'lll to 1|0, inclusive,

a yertical magnet 1|5, a rotary magnet 1|9, a

release magnet 120 and auxiliary control switch springs including the normal post s rings 125, the vertical off-normal springs 122, 1 3 and 120, and the 11th step cam or oir-normal springs '|28'.

The control equipment of this selector comprises a timing switch 140 of the well-known minor type, a line balancing coil 104 and a group of control relays.A More specifically, the relay equipment of the selector 100 includes a line or impulsing relay R160, a slow-acting hold relay R165, a slow-acting transfer relay R110, an automatic cut-in or stepping relay R180, a combined line test and line switching relay R150, a ringing control relay R190, a timer` start relay R195, a timer illustrated in Figs. 9 and 12 of the drawings.l Briefly described, this apparatus includes a voice current repeating coil 9|0, a combined talk and hold key |2|| of the locking type, a trunk busy lamp |201, an answer lamp |200, an incoming call buzzer |203, an operators telephone set l2l0, a battery feed coil |205 and a group of control relays. 'Ihese relays include a simplex controlled line relay R900, a hold relay R910, a digit absorbing relay R980, a ring-back or supervisory relay R905, a slow-to-operate line switching relay R990, a slow-acting supervisory control relay R930, a signal control relay R|200 and a night transfer relay R950. If desired, two keys may be I used in lieu of the single key |2| these two keys being utilized for talk and hold functions, re-

spectively.

The details of the access circuit |000 and associated delay operators position equipment are partially illustrated in Figs. 10` and 11 of the drawings as comprising a voice current repeatingy coil |0|0, operators position equipment 96, a

` combined monitor and talk key H80 of the locking type, a release key ||9| of the non-locking type, a trunk busy lamp H95, a line lamp H93, a

spervisory lamp H94 and a group of control relays.- This group of relays includes a simplex controlled line relay R|055, a slow-to-operate hold relay RI010, a digit` absorbing relay RI080, a` disconnect relay R|090, a ring-back relay R|000', a pair of slow-acting supervisory relays R|055 and Ri05, the last of which is of the differentiallywound type, a slow-'acting differentially wound pad switching control relay RI 050,

a line seizure relay R|060, a night transfer relay R|030, a split relay RI I I0, an answer relay RI |20, a supervisory relay Rl |35, a line switching relay Rl |10 and a pair of additional control relays RI |25 and R |30. The manner in which the various enumerated relays are connected and above, is shown in Fig. 2 of the drawings as comf prisingja timing switch 250 of the well-known minor type, a plurality of alarm leads C23|, C232, etc., a plurality -of alarm signal lamps 2|3, 2|4, etc., individually associated with the alarm leads, a plurality of alarm relaysR220, R225, etc., also individually associated with the alarm leads, and

a group of auxiliary control relays R2|0, R240 v vand R250. This equipment also includes van interrupter 231 ofthe motor-driven type for transmitting timing pulses tothe minor switch 2,50, a normally energized sig nal lamp 235, an alarm signal bell 236, and a reset key 233.

CAI-.L ro CENTRAL EXCHANGE 20 FROM 'rnE REMOTE ExcHANoE 30 tral exchange trunks, such, for example, as the 'trunk 440. When this trunk is seized, negative battery potential is impressed upon the two conductors thereof. 'I'he line relay R|300 ofthe toll line circuit 442 is thus energized. More speciilcally, the two lower windings of this relay are ena ergized over a circuit which extends from ground through the resistor |302, the two series connected lower windings o f R|300 and the two repeating coil windings |33| and |362 in parallel to battery as impressed upon the two sides of the trunk 440. relay R|300 is further energized over a circuit y which extends from ground by way of the contacts |3|2, the winding of the retard coil |304, the intermediate winding of R|300Aand the two rrepeating coil windings, |35| and |352 in parallel to battery as impressed upon the two sides of the trunk 440. It will be observed that the upper winding of the line relay R|300 is normally energized over a circuit including the resistor |303. Accordingly, this relay is exceedingly sensitive to changes in the energization of its two lower windings. When these two windings are energized over the circuits traced above, the relay,R|300 operates to complete, at its contacts |30l, a circuit for energizingthe relay R|340 in series with the winding of the line or pulsing relay R535 embodied in the toll transmission selector 300. One branch of this circuit extends from groun by way of the. contacts |30|, the winding yof R|343, the resistor |350, the upper winding of the line balancing coil |353, C45I, the contacts 32|, the repeating coil winding 3| the resistors 30|, 303 and 304, C332, the winding of R535 and the contacts 524 to battery. The other branch of this circuit extends from ground by way of the contacts |30i, the

R535 and the contacts 524 to battery. When energized over this simplex circuit, the relay R|340 operates to complete, at its contacts |34|, an obvious circuit for energizing the slow-to-release talking conductors C45| and C452 of the trunk 450 incoming to the toll transmission selector 330. At -its contacts |323, the relay R|320 connects the absorbing networwk comprising the condenser |303 and the resistor |301 in shunt with the winding of the series relay R|340. At its contacts |324, the relay R|320 completes an obvious circuit for energizing the relay R|350.

The relay R|350, upon operating,- closes its v contacts |35| to complete an obvious path for impath for impressing negative. battery potential.

pressing ground potential upon the control conductor C453 of the trunk 450. At its contacts |354. the relayRI350 completes a path including the contacts |33|` forimpressing ground potential upon the pad switching relay control lead C|303. thereby to short-circuit the pad switch- Xilng relay, conventionally embodied in the pad circuit |310. At its contacts |355. the relay R|350 opens a point in the normally completed upon the indicated pad switching relay control lead. Thus, the relay R|350, in operating, de energizes the pad switching relay of the circuit |310 so that the resistance pad of this circuitA is rendered eilective. 1n this regard it is pointed out above that the usual vacuum tube repeating equipment is provided at appropriately spaced intervals along the trunk 440 for increasing the voice ,current transmission level in both directions in order to maintain satisfactory voice current transmission over this trtmk. In accordance with conventional practice, theterminating pad embodied in the circuit |310 is of the resistive type and is associated with the repeat- \ing coil |330 for the purpose of controlling the The intermediate windings of thetransmission level over connections including the trunk ,440. Thus, if a call routed over this trunk is vto be extendedthrough the central exchage 20 to a distant exchange, more amplification, i. e.,

40 a higher voice current transmission level, is required than if the call is to be terminated locally at a substation served by the switching equipment of the central exchange. On a cali of the ilrst type, therefore, it is desirable to render the vresistance pad ineffective by controlling the pad switching relay of the network |310 to exclude the resistance pad from the voice current transmission channel. On the other hand, if the call bis to be terminatedlocally at the central ex- |313, the pad control relay R|330 is provided.

through the contacts las: nnrL oo series connected resistors |353 and |331.' Thus,.

It will be noted that when the relay R|350 operates in the manner explained above, the windingof the pad control relay R|330 is bridged A|353 across the the winding of the relay R|330 is, in eil'ect. connectd across opposite terminals of a resistance bridge, two arms of which'oomprise the resistors |353,and |351, respectively. 'I'he third arm -of 55 the bridge includes the upper winding of the hold relay R|320. lThe relay R|320, in operating,4 closesits contacts |32| and |322sto connect the une terminals of the repeating con windings ma and |354 through the pad circuit |310 t0 the ,resistance values of the circuit elements included in the two branches of the above-traced simplex circuit are so proportioned that the bridge is balanced and no potential difference is produced across the winding of the pad control relay R|330. The relay R|330 is thus prevented from operating. If it is desired to operate'the pad control relay in response to seizure of the toll transmission selector 300, the upper terminal of the resistor 304 may be disconnected from the center tap of the resistor 303 and connected to the upper terminal of the resistor 303. In such case, the voltage drop between the positive trunk conductor C452- and the upper terminal of the resistor 303, resulting from ground current over the above-traced simplex circuit is greater than the voltage drop between the trunk conductor C45| and the upper terminal of the resistor 303. Accordingly, the bridge is unbalanced and a diierence of potential is produced across the winding of the pad control relay R|330, causing this relay to operate. Inoperatng, the relay R|330 opens its contacts |33| to interrupt the abovemission channel connecting the inter-office trunkte!) with the trunk 550.

When energized over the above-traced simplex circuit, the line relay R535 of the toll transmission selector 300 operates and, at its contacts 536, opens a point in the circuit for energizing the release magnet 523. At its contacts 531, the relay R535 completes an obvious circuit for energizing the slow-to-release hold relay R505. At its contacts 536, the relay R535 prepares a circuit for repeating impulses over the line wipers 5H and 5|2 of the switching mechanism 5|0 to the trunk extending to a succeeding numerical switch.

The hold relay R565, upon operating, opens its contacts 568, thereby further to interrupt the circuit for energizing the release magnet 523, and prepares, at its contacts 551, a circuit for energizing the transfer relay R560 in parallel with the vertical magnet 520. At its cont-acts 566, the relay R555 completes a path including the contacts 5M for impressing ground potential upon the alarm conductor (323|. The purpose ofthe arrangement for grounding the alarm conductor 023| when the toll transmission selector 300 is seized is described with particularity hereinafter.

, Following the operation of the line and hold relays R535 and R545, respectively, the selector 300 is conditioned to respond to the impulses comprising the first digit of the directory number designating the desired operator in the central cnice, or the desired subscriber line terminating at the central oice. A

During the operation o'i the impulse sending device provided at the toll operators position 54| in the remote exchange 30 and utilized to transmit impulses overthe trunk 650, the line relay RI 300 functions to repeat the impulses over the established simplex circuit to the line relay R535. Accordingly, the latter relay is caused to follow une impulses transmitted over the trunk 630 from the toll operators position 44|. This relay, upon restoring at the beginning of thev open-circuit period of the rst impulse, opens its contacts 531 to interrupt the operating circuit for the hold relay R555. The latter relay, due

to its slow-torelease characteristic, remains operated during impulsing. At its contacts 530, the relay R535 completes the above-mentioned circuit forv energizing the transfer relay R560 and thevertical magnet 520 in parallel. One branch of this circuit extends from ground by way of the contacts 538 and 541, and the winding of R560 ,to battery. The other branch of this circuit extends from ground by way of the contacts 538, 561 and 556, and the winding of the mag- \net 520 to battery. The relay R560, upon operating, closes its contacts 56| to complete a path including the resistor 505 and the two conductors C311 and C310 in shunt with the upper Winding of the control relay R310. At its contacts 563, the relay R560 opens a point in the operating circuit for the rotary magnet 526. At its contacts 562, the relay R560 completes an obvi vertical direction each time the line relay R535 restores to complete its operating circuit as traced above. When these vwipers are moved oi normal, the vertical o-normal springs 39|, 332 and 333 are respectively operated into engagement. At the contact springs 392, the circ uit for energizing the release magnet 523 is prepared. At the contacts 333, a circuit is prepared for energizing the stepping relay.R510. At thev contacts 39|, a circuit including the conductor C383 is completed for energizing the supervisory relay R550. The relay R540, upon operating, completes a, multiple path including the contacts 566 and 562 for impressing ground potential upon the control conductor C453. At its contacts 552, the-relay R560 also completes the prepared operating circuit for the stepping relay R510, this circuit extending from ground by way of the contacts 535, 553,555 and 562, the Winding of R510, C383. the oE-normal springs 393, the

grounding the supervisory lead C505,

The stepping relay R510 operates when enererating, locks to ground over a path including the contacts 522 and 51|. ,At its contacts 512, the relay R510 prepares the .operating circuit for the rotary magnet 52|. Following the operations just described, the wipers 5H to 5M, inclusive, are elevated step byA step under the control of the vertical magnet 520, so that at the conclusion of the digit they are positioned opposite the level of bank contacts terminating the group of trunks which correspond to the numerical value of the digit. In this regard it will be understood that the numerical value of the digit determines the path which the call will take. 

